Common-rail fuel-injection system

Abstract

Disclosed is a common-rail fuel injection system which regulates an amount of fuel delivered at every plunger in a high-pressure fuel-supply pump, thereby enabling to control an actual common-rail pressure restored at every fuel delivery forced by the plunger so as to come in matching a desired common-rail pressure. A fundamental desired amount of fuel delivered is found dependent on the desired common-rail pressure derived from the engine operating conditions. A correction amount of fuel delivered is calculated at every plunger on the basis of a deviation in the common-rail pressure, which is derived from the actual common-rail pressure restored with the fuel delivery and sensed at every fuel delivery. Each plunger delivers under pressure an ultimate amount of fuel that is compensated with the correction amount of fuel delivered, thereby making the common-rail pressure coincide with the desired common-rail pressure.

What is claimed is:  
     
       1. A common-rail fuel-injection system for an internal combustion engine; comprising a fuel supply pump to deliver fuel with pumping action of a plunger, a common rail to store therein the fuel delivered out of the fuel supply pump under pressure, injectors each of which is arranged in each cylinder of the engine, to inject the fuel in the common rail into the cylinders, sensor means to monitor engine operating conditions, a pressure sensor to monitor a pressure in the common rail, and a control unit to find injection factors, including a desired common-rail pressure, of fuel to be injected out of the injectors, depending on signals reported from the sensor means, and further control a fuel delivery forced by the plunger in the fuel supply pump and a fuel injection out of the injector in accordance with the injection factors; 
       wherein the pressure sensor detects an actual common-rail pressure at the time between pressure restoration with the fuel delivered by the plunger and pressure drop due to fuel injection out of the injector, and the control unit compensates an amount of fuel to be delivered into the common rail, depending on a deviation of the actual common-rail pressure from the desired common-rail pressure, at every fuel delivery forced by the plunger, so that the actual common-rail pressure coincides with the desired common-rail pressure.  
     
     
       2. A common-rail fuel-injection system constructed as defined in claim  1 , wherein the control unit finds a fundamental desired amount of fuel to be delivered by the plunger in accordance with the desired common-rail pressure, compensates the fundamental desired amount of fuel to be delivered with a correction amount of fuel which is calculated dependent on the deviation of the actual common-rail pressure, thereby finding an ultimate desired amount of fuel delivered at every fuel delivery forced by the plunger, and regulates a fuel delivery duration to be delivered by the plunger in accordance with the ultimate desired amount of fuel to make the actual common-rail pressure coincide with the desired common-rail pressure. 
     
     
       3. A common-rail fuel-injection system constructed as defined in claim  1 , wherein the fuel supply pump has plural plungers, each of which is operable correspondingly to the individual injection of the injector arranged in each cylinder. 
     
     
       4. A common-rail fuel-injection system constructed as defined in claim  1 , wherein the fuel supply pump is comprised of the plunger moving in and out inside a pump barrel, a cam mounted on a pump-drive shaft to push the plunger so as to deliver the fuel trapped in a pumping chamber that is defined by the plunger and the pump barrel, a fuel passage to lead the fuel into the pumping chamber, and an inlet valve to either open or block a fluid communication between the pumping chamber and the fuel passage, and wherein the control unit closes the inlet valve at preselected timing during a lift stroke of the plunger to regulate an amount of fuel to be returned to the fuel passage out of the fuel admitted in the pumping chamber, thereby governing the amount of fuel to be delivered under pressure out of the pumping chamber. 
     
     
       5. A common-rail fuel-injection system constructed as defined in claim  4 , wherein a pressure-control chamber is provided by a valve body of the inlet valve and a valve cylinder in which the valve body moves in and out, while a control valve is arranged to either open or block a fluid communication between the pressure control chamber and the fuel passage, so that opening the control valve results in connecting the pressure control chamber with the fuel passage in a fluid communication to allow the inlet valve to move in and out, whereas closing the control valve results in blocking the fluid communication between the pressure control chamber and the fuel passage to keep the inlet valve against moving in and out.